// Source : https://www.geeksforgeeks.org/bitonic-sort/

/* C++ Program for Bitonic Sort. Note that this program 
   works only when size of input is a power of 2. */
   
#include<stdio.h>
#include<algorithm.h>
using namespace std; 
  
/*The parameter dir indicates the sorting direction, ASCENDING 
   or DESCENDING; if (a[i] > a[j]) agrees with the direction, 
   then a[i] and a[j] are interchanged.*/
void compAndSwap(int a[], int i, int j, int dir) 
{ 
    if (dir==(a[i]>a[j])) 
        swap(a[i],a[j]); 
} 
  
/*It recursively sorts a bitonic sequence in ascending order, 
  if dir = 1, and in descending order otherwise (means dir=0). 
  The sequence to be sorted starts at index position low, 
  the parameter cnt is the number of elements to be sorted.*/
void bitonicMerge(int a[], int low, int cnt, int dir) 
{ 
    if (cnt>1) 
    { 
        int k = cnt/2; 
        for (int i=low; i<low+k; i++) 
            compAndSwap(a, i, i+k, dir); 
        bitonicMerge(a, low, k, dir); 
        bitonicMerge(a, low+k, k, dir); 
    } 
} 
  
/* This function first produces a bitonic sequence by recursively 
    sorting its two halves in opposite sorting orders, and then 
    calls bitonicMerge to make them in the same order */
void bitonicSort(int a[],int low, int cnt, int dir) 
{ 
    if (cnt>1) 
    { 
        int k = cnt/2; 
  
        // sort in ascending order since dir here is 1 
        bitonicSort(a, low, k, 1); 
  
        // sort in descending order since dir here is 0 
        bitonicSort(a, low+k, k, 0); 
  
        // Will merge wole sequence in ascending order 
        // since dir=1. 
        bitonicMerge(a,low, cnt, dir); 
    } 
} 
  
/* Caller of bitonicSort for sorting the entire array of 
   length N in ASCENDING order */
void sort(int a[], int N, int up) 
{ 
    bitonicSort(a,0, N, up); 
} 
  
// Driver code 
int main() 
{ 
    int a[]= {3, 7, 4, 8, 6, 2, 1, 5}; 
    int N = sizeof(a)/sizeof(a[0]); 
  
    int up = 1;   // means sort in ascending order 
    sort(a, N, up); 
  
    printf("Sorted array: \n"); 
    for (int i=0; i<N; i++) 
        printf("%d ", a[i]); 
    return 0; 
}
